Has Europe been in the Western Alliance in the past 2 decades? The US has been shouldering the costs of this alliance while all Europe does is criticize the US while giving empty promises for military investments. This weakness opened the door for Putin to invade Ukraine, something he would never done if Europe had done what it promised. Trump was literally laughed at in Germany when he complained of its reliance on Russian natural gas combined with its weak military investments.
The US has been giving this feedback for over a decade. While I don't necessarily support the President's posture, it took these extreme measures for Europe to start listening. Europe and US are natural allies, but it must be an actual alliance.